BBC flagship children's shows Blue Peter and Newsround have been damaged by the transfer of Anne Robinson quiz show The Weakest Link to BBC1, a report by the BBC Trust has said.

The corporation's regulator found that the bumping forward of afternoon childrens' programmes on BBC1 by 20 minutes to accommodate the "mean" quiz had led to viewing figures declining for them "significantly".

The Weakest Link, which is hosted by Robinson in customary black garb and features contestants voting each other off, was moved from BBC2 in February last year to fill the afternoon slot left empty when Australian soap Neighbours was poached by Channel Five in a multimillion-pound deal.

However, because The Weakest Link airs in 45-minute instalments compared with Neighbours' 25 minutes, children's shows on BBC1 were shifted forward, meaning key programmes such as Blue Peter and Newsround – which are aimed at older children – start before many of their potential viewers are home from school.

As a result, the trust said that ratings for the two shows had fallen from around 300,000 an episode in 2003 to 200,000 in 2007.

In a review of children's output, to be published today, the trust said the shows made an important contribution to the BBC's "citizenship and global public purposes" aims – but their declining ratings had been "exacerbated" by schedule changes.

The trust said that in future, scheduling decisions should "prioritise children's output unless there is a strong public value reason for not doing so" and called on BBC management to boost audience numbers for the shows – although it stopped short of demanding The Weakest Link should be moved.

A spokeswoman for BBC management said there were no plans to move the quiz show but that other options to boost ratings would be looked at, with a plan to be drawn up by the summer. It is thought this could involve revamping the shows or commissioning "more exciting" content.

The report also said that ratings for Saturday morning children's programmes had also fallen "significantly" and not recovered since they were moved from BBC1 to BBC2 in early 2006 to make way for cooking and lifestyle shows.

BBC trustee Mehmuda Mian, who led the review, said: "We have asked the executive to address this decline and, as far as possible, to make sure that programmes for children are given priority at times children are likely to be watching."

The report also called for a change in arrangements for children's audio, saying ratings for radio shows on Radio 4 and BBC7 were too low.

It also warned that the BBC could go too far with its new "fewer, bigger, better" strategy of commissioning fewer shows that are of higher quality. The report said some children had complained about too many repeats while it also said smaller production companies could be edged out of the BBC.

The review praised the BBC's overall commitment to children's programming, saying the corporation must remain a "cornerstone" of high-quality UK-produced content, adding that its output "generally outperformed commercial providers in terms of usage levels and quality measures".

Jana Bennett, the BBC Vision director, said: "The BBC's children's services are a great success story devoted to providing creativity and dedicated to enriching children's lives."

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